2. Release row in Domain_Site_Sync by having _var_id_domain_site.
This ensures that the row with _var_id_domain_site cannot be fetched in section 1 (see above), because it is being excluded logically when we set dss.`lock` = 1

Why dreadlocks are there?
By my mind, updates use different indexes, dont use one primarykey id, and logically all rows, that fetched in section 1, cannot be fetched until they won't be released in section 2